The present invention is concerned with a structure for avoiding or eliminating polymer from bleeding into optical fiducial holes on a substrate. The present invention is especially concerned with providing a plurality of holes surrounding at least substantially one half of an optical fiducial hole. This provides for collecting any polymer flowing towards the optical fiducial hole prior to it reaching the hole.
In the manufacture of integrated circuit chip carriers, a dielectric sheet material is employed as the substrate, and in many cases is a laminated polymeric substrate of a plurality of layers. In order to provide electrical connection between layers, metal coated through-holes are provided. The plated through-holes are typically filled with a conductive polymeric paste or with polymer from the prepreg used in the lamination to form the dielectric sheet material. Typical compositions include copper-epoxy paste compositions or epoxy resin compositions used in fabricating the prepreg.
It is required that the holes which will be plated and are intended to serve as the functional holes or plated through-holes as well as optical fiducial holes be provided such as by drilling together in order to maintain a true reference during the remainder of the carrier processing.
Furthermore, in order to achieve good optical registration during circuitization, the optical fiducial holes must not become filled with resin composition employed in filling the plated through-holes. However, the optical fiducial holes are in close proximity to various functional holes and therefore a tendency exists for the resin during the hole-fill-lamination process to bleed into the optical fiducial holes. Accordingly, it would be desirable to prevent the resin bleed from filling the optical fiducial holes.
The present invention makes it possible to avoid or exclude the polymer bleed from filling the optical fiducial holes. In particular, the present invention prevents the optical fiducial holes from being filled with polymer bleed by providing a plurality of holes that surround at least substantially one-half of the optical fiducial hole. This plurality of holes is located between the optical fiducial holes and the functional plated through-holes. Accordingly, this plurality of holes prevents the resin from entering the optical fiducial holes, thereby assuring that automated optical art work registration can be carried out.
Accordingly, one aspect of the present invention relates to a substrate comprising at least one optical fiducial hole and a plurality of holes surrounding at least substantially one-half of the at least one optical fiducial hole.
The present invention also relates to a method for preventing the filling of optical fiducial holes which comprises providing a plurality of holes for use as functional holes and at least one optical fiducial hole in a substrate; providing a plurality of holes surrounding at least substantially one-half of the at least one optical fiducial hole, and being located between the functional holes and the at least one optical fiducial hole. The functional holes are then filled with polymer composition.
Still other objects and advantages of the present invention will become readily apparent by those skilled in the art from the following detailed description, wherein it is shown and described only the preferred embodiments of the invention, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, without departing from the invention. Accordingly, the description is to be regarded as illustrative in nature and not as restrictive.
FIG. 1 is a top view illustrating a portion of an integrated circuit chip carrier.
FIG. 2 illustrates an array of holes surrounding an optical fiducial hole according to the present invention.
FIG. 3 is an alternative array of holes surrounding an optical fiducial hole according to the present invention.
FIG. 4 is another alternative array of holes surrounding an optical fiducial hole according to the present invention.
FIG. 5 is a further alternative array of holes surrounding an optical fiducial hole according to the present invention.